Support text decoration in QPainter::drawGlyphs()

In order to support text decorations (overline, underline and strikeout)
in QPainter::drawGlyphs(), we need to call drawTextItemDecoration()
from this function. To support this, it has been generalized to no
longer require a QTextItemInt. We also need to propagate the decoration
attributes of the font from QTextLayout to QGlyphs, since this is not
part of the QFontEngine.

Task-number: QTBUG-12122
Reviewed-by: Kim

3 files changed, 208 insertions, 22 deletions

diff --git a/src/gui/painting/qpainter.cpp b/src/gui/painting/qpainter.cpp
index a845842..d6fbab3 100644
--- a/src/gui/painting/qpainter.cpp
+++ b/src/gui/painting/qpainter.cpp
@@ -88,6 +88,10 @@ bool qt_show_painter_debug_output = true;
 
 extern QPixmap qt_pixmapForBrush(int style, bool invert);
 
+static void drawTextItemDecoration(QPainter *painter, const QPointF &pos, QFontEngine *fe,
+                                   QTextCharFormat::UnderlineStyle underlineStyle,
+                                   QTextItemInt::RenderFlags flags, qreal width,
+                                   const QTextCharFormat &charFormat);
 void qt_format_text(const QFont &font,
                     const QRectF &_r, int tf, const QTextOption *option, const QString& str, QRectF *brect,
                     int tabstops, int* tabarray, int tabarraylen,
@@ -5750,6 +5754,8 @@ void qt_draw_glyphs(QPainter *painter, const quint32 *glyphArray, const QPointF
 
 void QPainterPrivate::drawGlyphs(quint32 *glyphArray, QFixedPoint *positions, int glyphCount)
 {
+    Q_Q(QPainter);
+
     updateState(state);
 
     QFontEngine *fontEngine = state->font.d->engineForScript(QUnicodeTables::Common);
@@ -5764,6 +5770,26 @@ void QPainterPrivate::drawGlyphs(quint32 *glyphArray, QFixedPoint *positions, in
         fontEngine = static_cast<QFontEngineMulti *>(fontEngine)->engine(engineIdx);
     }
 
+    QFixed leftMost;
+    QFixed rightMost;
+    QFixed baseLine;
+    for (int i=0; i<glyphCount; ++i) {
+        glyph_metrics_t gm = fontEngine->boundingBox(glyphArray[i]);
+        if (i == 0 || leftMost > positions[i].x)
+            leftMost = positions[i].x;
+
+        // We don't support glyphs that do not share a common baseline. If this turns out to
+        // be a relevant use case, then we need to find clusters of glyphs that share a baseline
+        // and do a drawTextItemDecorations call per cluster.
+        if (i == 0 || baseLine < positions[i].y)
+            baseLine = positions[i].y;
+
+        // We use the advance rather than the actual bounds to match the algorithm in drawText()
+        if (i == 0 || rightMost < positions[i].x + gm.xoff)
+            rightMost = positions[i].x + gm.xoff;
+    }
+
+    QFixed width = rightMost - leftMost;
 
     if (extended != 0) {
         QStaticTextItem staticTextItem;
@@ -5797,6 +5823,21 @@ void QPainterPrivate::drawGlyphs(quint32 *glyphArray, QFixedPoint *positions, in
 
         engine->drawTextItem(QPointF(0, 0), textItem);
     }
+
+    QTextItemInt::RenderFlags flags;
+    if (state->font.underline())
+        flags |= QTextItemInt::Underline;
+    if (state->font.overline())
+        flags |= QTextItemInt::Overline;
+    if (state->font.strikeOut())
+        flags |= QTextItemInt::StrikeOut;
+
+    drawTextItemDecoration(q, QPointF(leftMost.toReal(), baseLine.toReal()),
+                           fontEngine,
+                           (state->font.underline()
+                                ? QTextCharFormat::SingleUnderline
+                                : QTextCharFormat::NoUnderline),
+                           flags, width.toReal(), QTextCharFormat());
 }
 
 /*!
@@ -6322,15 +6363,15 @@ static QPixmap generateWavyPixmap(qreal maxRadius, const QPen &pen)
     return pixmap;
 }
 
-static void drawTextItemDecoration(QPainter *painter, const QPointF &pos, const QTextItemInt &ti)
+static void drawTextItemDecoration(QPainter *painter, const QPointF &pos, QFontEngine *fe,
+                                   QTextCharFormat::UnderlineStyle underlineStyle,
+                                   QTextItemInt::RenderFlags flags, qreal width,
+                                   const QTextCharFormat &charFormat)
 {
-    QTextCharFormat::UnderlineStyle underlineStyle = ti.underlineStyle;
     if (underlineStyle == QTextCharFormat::NoUnderline
-        && !(ti.flags & (QTextItem::StrikeOut | QTextItem::Overline)))
+        && !(flags & (QTextItem::StrikeOut | QTextItem::Overline)))
         return;
 
-    QFontEngine *fe = ti.fontEngine;
-
     const QPen oldPen = painter->pen();
     const QBrush oldBrush = painter->brush();
     painter->setBrush(Qt::NoBrush);
@@ -6339,7 +6380,7 @@ static void drawTextItemDecoration(QPainter *painter, const QPointF &pos, const
     pen.setWidthF(fe->lineThickness().toReal());
     pen.setCapStyle(Qt::FlatCap);
 
-    QLineF line(pos.x(), pos.y(), pos.x() + ti.width.toReal(), pos.y());
+    QLineF line(pos.x(), pos.y(), pos.x() + width, pos.y());
 
     const qreal underlineOffset = fe->underlinePosition().toReal();
     // deliberately ceil the offset to avoid the underline coming too close to
@@ -6354,21 +6395,21 @@ static void drawTextItemDecoration(QPainter *painter, const QPointF &pos, const
         painter->save();
         painter->translate(0, pos.y() + 1);
 
-        QColor uc = ti.charFormat.underlineColor();
+        QColor uc = charFormat.underlineColor();
         if (uc.isValid())
             pen.setColor(uc);
 
         // Adapt wave to underlineOffset or pen width, whatever is larger, to make it work on all platforms
         const QPixmap wave = generateWavyPixmap(qMax(underlineOffset, pen.widthF()), pen);
-        const int descent = (int) ti.descent.toReal();
+        const int descent = (int) fe->descent().toReal();
 
         painter->setBrushOrigin(painter->brushOrigin().x(), 0);
-        painter->fillRect(pos.x(), 0, qCeil(ti.width.toReal()), qMin(wave.height(), descent), wave);
+        painter->fillRect(pos.x(), 0, qCeil(width), qMin(wave.height(), descent), wave);
         painter->restore();
     } else if (underlineStyle != QTextCharFormat::NoUnderline) {
         QLineF underLine(line.x1(), underlinePos, line.x2(), underlinePos);
 
-        QColor uc = ti.charFormat.underlineColor();
+        QColor uc = charFormat.underlineColor();
         if (uc.isValid())
             pen.setColor(uc);
 
@@ -6380,14 +6421,14 @@ static void drawTextItemDecoration(QPainter *painter, const QPointF &pos, const
     pen.setStyle(Qt::SolidLine);
     pen.setColor(oldPen.color());
 
-    if (ti.flags & QTextItem::StrikeOut) {
+    if (flags & QTextItem::StrikeOut) {
         QLineF strikeOutLine = line;
         strikeOutLine.translate(0., - fe->ascent().toReal() / 3.);
         painter->setPen(pen);
         painter->drawLine(strikeOutLine);
     }
 
-    if (ti.flags & QTextItem::Overline) {
+    if (flags & QTextItem::Overline) {
         QLineF overLine = line;
         overLine.translate(0., - fe->ascent().toReal());
         painter->setPen(pen);
@@ -6528,7 +6569,8 @@ void QPainter::drawTextItem(const QPointF &p, const QTextItem &_ti)
         else
             d->engine->drawTextItem(p, ti);
     }
-    drawTextItemDecoration(this, p, ti);
+    drawTextItemDecoration(this, p, ti.fontEngine, ti.underlineStyle, ti.flags, ti.width.toReal(),
+                           ti.charFormat);
 
     if (d->state->renderHints != oldRenderHints) {
         d->state->renderHints = oldRenderHints;
diff --git a/src/gui/text/qtextlayout.cpp b/src/gui/text/qtextlayout.cpp
index 3bad6a5..4dda114 100644
--- a/src/gui/text/qtextlayout.cpp
+++ b/src/gui/text/qtextlayout.cpp
@@ -2183,13 +2183,15 @@ static void setPenAndDrawBackground(QPainter *p, const QPen &defaultPen, const Q
 namespace {
     struct GlyphInfo
     {
-        GlyphInfo(const QGlyphLayout &layout, const QPointF &position)
-            : glyphLayout(layout), itemPosition(position)
+        GlyphInfo(const QGlyphLayout &layout, const QPointF &position,
+                  const QTextItemInt::RenderFlags &renderFlags)
+            : glyphLayout(layout), itemPosition(position), flags(renderFlags)
         {
         }
 
         QGlyphLayout glyphLayout;
         QPointF itemPosition;
+        QTextItem::RenderFlags flags;
     };
 }
 
@@ -2218,6 +2220,15 @@ QList<QGlyphs> QTextLine::glyphs() const
         QPointF pos(iterator.x.toReal(), y);
 
         QFont font = eng->font(si);
+
+        QTextItem::RenderFlags flags;
+        if (font.overline())
+            flags |= QTextItem::Overline;
+        if (font.underline())
+            flags |= QTextItem::Underline;
+        if (font.strikeOut())
+            flags |= QTextItem::StrikeOut;
+
         QGlyphLayout glyphLayout = eng->shapedGlyphs(&si).mid(iterator.glyphsStart,
                                                               iterator.glyphsEnd - iterator.glyphsStart);
 
@@ -2235,7 +2246,7 @@ QList<QGlyphs> QTextLine::glyphs() const
 
                     QGlyphLayout subLayout = glyphLayout.mid(start, end - start);
                     glyphLayoutHash.insertMulti(multiFontEngine->engine(which),
-                                                GlyphInfo(subLayout, pos));
+                                                GlyphInfo(subLayout, pos, flags));
 
                     start = end;
                     which = e;
@@ -2243,16 +2254,16 @@ QList<QGlyphs> QTextLine::glyphs() const
 
                 QGlyphLayout subLayout = glyphLayout.mid(start, end - start);
                 glyphLayoutHash.insertMulti(multiFontEngine->engine(which),
-                                            GlyphInfo(subLayout, pos));
+                                            GlyphInfo(subLayout, pos, flags));
 
             } else {
                 glyphLayoutHash.insertMulti(mainFontEngine,
-                                            GlyphInfo(glyphLayout, pos));
+                                            GlyphInfo(glyphLayout, pos, flags));
             }
         }
     }
 
-    QHash<QFontEngine *, QGlyphs> glyphsHash;
+    QHash<QPair<QFontEngine *, int>, QGlyphs> glyphsHash;
 
     QList<QFontEngine *> keys = glyphLayoutHash.uniqueKeys();
     for (int i=0; i<keys.size(); ++i) {
@@ -2265,6 +2276,11 @@ QList<QGlyphs> QTextLine::glyphs() const
         for (int j=0; j<glyphLayouts.size(); ++j) {
             const QPointF &pos = glyphLayouts.at(j).itemPosition;
             const QGlyphLayout &glyphLayout = glyphLayouts.at(j).glyphLayout;
+            const QTextItem::RenderFlags &flags = glyphLayouts.at(j).flags;            
+
+            font.setOverline(flags.testFlag(QTextItem::Overline));
+            font.setUnderline(flags.testFlag(QTextItem::Underline));
+            font.setStrikeOut(flags.testFlag(QTextItem::StrikeOut));
 
             QVarLengthArray<glyph_t> glyphsArray;
             QVarLengthArray<QFixedPoint> positionsArray;
@@ -2283,10 +2299,12 @@ QList<QGlyphs> QTextLine::glyphs() const
             glyphIndexes.setGlyphIndexes(glyphs);
             glyphIndexes.setPositions(positions);
 
-            if (!glyphsHash.contains(fontEngine))
-                glyphsHash.insert(fontEngine, QGlyphs());
+            QPair<QFontEngine *, int> key(fontEngine, int(flags));
+
+            if (!glyphsHash.contains(key))
+                glyphsHash.insert(key, QGlyphs());
 
-            QGlyphs &target = glyphsHash[fontEngine];
+            QGlyphs &target = glyphsHash[key];
             target += glyphIndexes;
             target.setFont(font);
         }
diff --git a/tests/auto/qglyphs/tst_qglyphs.cpp b/tests/auto/qglyphs/tst_qglyphs.cpp
index 54a69dc..6827b23 100644
--- a/tests/auto/qglyphs/tst_qglyphs.cpp
+++ b/tests/auto/qglyphs/tst_qglyphs.cpp
@@ -66,6 +66,9 @@ private slots:
     void drawNonExistentGlyphs();
     void drawMultiScriptText1();
     void drawMultiScriptText2();
+    void drawStruckOutText();
+    void drawOverlinedText();
+    void drawUnderlinedText();
     void detach();
 
 private:
@@ -401,6 +404,129 @@ void tst_QGlyphs::detach()
     QCOMPARE(glyphs.glyphIndexes(), QVector<quint32>() << 1 << 2 << 3);
 }
 
+void tst_QGlyphs::drawStruckOutText()
+{
+    QPixmap textLayoutDraw(1000, 1000);
+    QPixmap drawGlyphs(1000, 1000);
+
+    textLayoutDraw.fill(Qt::white);
+    drawGlyphs.fill(Qt::white);
+
+    QString s = QString::fromLatin1("Foobar");
+
+    QFont font;
+    font.setStrikeOut(true);
+
+    QTextLayout layout(s);
+    layout.setFont(font);
+    layout.beginLayout();
+    layout.createLine();
+    layout.endLayout();
+
+    {
+        QPainter p(&textLayoutDraw);
+        layout.draw(&p, QPointF(50, 50));
+    }
+
+    QGlyphs glyphs = layout.glyphs().size() > 0
+                                 ? layout.glyphs().at(0)
+                                 : QGlyphs();
+
+    {
+        QPainter p(&drawGlyphs);
+        p.drawGlyphs(QPointF(50, 50), glyphs);
+    }
+
+#if defined(DEBUG_SAVE_IMAGE)
+    textLayoutDraw.save("drawStruckOutText_textLayoutDraw.png");
+    drawGlyphs.save("drawStruckOutText_drawGlyphIndexes.png");
+#endif
+
+    QCOMPARE(textLayoutDraw, drawGlyphs);
+}
+
+void tst_QGlyphs::drawOverlinedText()
+{
+    QPixmap textLayoutDraw(1000, 1000);
+    QPixmap drawGlyphs(1000, 1000);
+
+    textLayoutDraw.fill(Qt::white);
+    drawGlyphs.fill(Qt::white);
+
+    QString s = QString::fromLatin1("Foobar");
+
+    QFont font;
+    font.setOverline(true);
+
+    QTextLayout layout(s);
+    layout.setFont(font);
+    layout.beginLayout();
+    layout.createLine();
+    layout.endLayout();
+
+    {
+        QPainter p(&textLayoutDraw);
+        layout.draw(&p, QPointF(50, 50));
+    }
+
+    QGlyphs glyphs = layout.glyphs().size() > 0
+                                 ? layout.glyphs().at(0)
+                                 : QGlyphs();
+
+    {
+        QPainter p(&drawGlyphs);
+        p.drawGlyphs(QPointF(50, 50), glyphs);
+    }
+
+#if defined(DEBUG_SAVE_IMAGE)
+    textLayoutDraw.save("drawOverlineText_textLayoutDraw.png");
+    drawGlyphs.save("drawOverlineText_drawGlyphIndexes.png");
+#endif
+
+    QCOMPARE(textLayoutDraw, drawGlyphs);
+}
+
+void tst_QGlyphs::drawUnderlinedText()
+{
+    QPixmap textLayoutDraw(1000, 1000);
+    QPixmap drawGlyphs(1000, 1000);
+
+    textLayoutDraw.fill(Qt::white);
+    drawGlyphs.fill(Qt::white);
+
+    QString s = QString::fromLatin1("Foobar");
+
+    QFont font;
+    font.setUnderline(true);
+
+    QTextLayout layout(s);
+    layout.setFont(font);
+    layout.beginLayout();
+    layout.createLine();
+    layout.endLayout();
+
+    {
+        QPainter p(&textLayoutDraw);
+        layout.draw(&p, QPointF(50, 50));
+    }
+
+    QGlyphs glyphs = layout.glyphs().size() > 0
+                                 ? layout.glyphs().at(0)
+                                 : QGlyphs();
+
+    {
+        QPainter p(&drawGlyphs);
+        p.drawGlyphs(QPointF(50, 50), glyphs);
+    }
+
+#if defined(DEBUG_SAVE_IMAGE)
+    textLayoutDraw.save("drawUnderlineText_textLayoutDraw.png");
+    drawGlyphs.save("drawUnderlineText_drawGlyphIndexes.png");
+#endif
+
+    QCOMPARE(textLayoutDraw, drawGlyphs);
+}
+
 QTEST_MAIN(tst_QGlyphs)
 #include "tst_qglyphs.moc"